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Ceramium tenuicorne (Kütz.) Wærn (including C. gobii Waern) is a common red alga in the Skagerrak-Baltic Sea region. A Polysiphonia-type of life history and asexual reproduction by paraspores, previously demonstrated in cultures for this species, have been confirmed. In addition, a characteristic kind of reproductive structure ("Gobi's monosporangia") has been described in field-collected material from the Baltic Sea. This type of structure was used to distinguish the new species Ceramium gobii.
Formation and function of "Gobi's monosporangia" were studied in culture and they are modified branch apices in which the cells are transformed directly into enlarged, rounded bodies that grew into a new generation of similar plants. They are referred to as vegetative propagules rather than sporangia. Tetrasporangia were sometimes found together with either parasporangia or vegetative propagules. The tetrasporangia usually failed to develop, but in a few cases mature gametophytes developed as well as plants with mixed spermatangia and parasporangia or spermatangia and vegetative propagules. Thus the interconnection between sexual and asexual modes of reproduction was demonstrated.
The Baltic Sea provides a unique model system for studying genetic effects of postglacial colonization and ecological differentiation, because all marine organism must have immigrated after the opening of the Danish Straits 8000 years ago and responded to the development of the steep Skagerrak-Baltic salinity gradient. The red alga Ceramium tenuicorne shows conspicuous variation in growth and reproduction along this gradient. We obtained reproductive data coupled with two types of molecular markers (cox2-3 spacer, mtDNA and random amplified polymorphic DNA, RAPDs). Five mtDNA haplotypes were observed, of which two highly divergent ones were common. One was restricted to and fixed in Oslofjorden, and the other, which was closely related to the three rare haplotypes, was found from southernmost Norway via Kattegat into the Baltic. The RAPD data revealed, on the other hand, a continuous cline corresponsing to the salinity gradient with most of the variation stores at the smallest spatial scale analysed (i.e. within 1 square meter subpopulations). The combined data suggests colonization from a diverse Atlantic gene pool followed by lineage sorting of ancestral mtDNA polymorphisms and strong differential selection among nuclear genotypes along the salinity gradient, including selction for non-recombinant multiplication of those best fit to the marginal low-salinity habitats.
Widely distributed species may often be divided into cryptic level taxonomic entities, for example temperature and/or salinity ecotypes. This also applies to the reproduction of Acinetospora crinita in which the many types of reproductive patterns are related to specific strains.
Experimental autecological studies are imperative prior to any hypotheses or conclusions on environmental impact, for example anthropogenous, on distribution and reproduction of individual species.
Growth and morphological responses to a decline in salinity was determined in culture for the tetrasporophyte and gametophytes of the red alga Aglaothamnion tenuissimum. Statistically significant differences in growth and cell dimensions were found between male and female gametophytes and between gametophytes and the tetrasporophyte. The results show that combinations of growth experiments and morphological investigations are needed to avoid confusion and erroneous biogeographic conclusions.
Furthermore, salinity response in growth and reproduction in Ceramium tenuicorne was investigated in three salinity regions along the salinity gradient from Skagerrak to the Baltic Sea area. The results show that the within population variation is low when the different reproductive types are examined separately. Tetrasporophytes showed significant variation between the three regions. The difference between parasporophytes from Skagerrak and Kattegat was not significant. Salinity response of "Gobi's monosporangia" or propagules suggests that they are not limited to their present geographic distribution.
In the green alga Enteromorpha intestinalis the within-variation in Baltic populations was low, while the opposite was the case in Kattegat, where the populations seem to consist of a mixture of plants with a so-called Kattegat response and a Baltic response. This indicates that migration/dispersal does occur within the Baltic Sea area.
The green alga Enteromorpha intestinalis is a cosmopolitan species that causes green tides in many coastal areas and is used as an indicator species for eutrophication in the Baltic Sea area.
We report on five polymorphic microsatellite markers developed from enriched genomic libraries. The number of alleles per locus ranged from 7 to 25.
As Enteromorpha intestinalis is an indicator for high nutrient levels in the Baltic Sea and elsewhere, microsatellites, which are useful markers of population substructures, are very important to address questions concerning eutrophication, fex. Are certain haplotypes favoured by high nutrient levels? Enteromorpha is a haploid-diploid species with both sexual and asexual reproduction. Our results illuminate the spatial and temporal variation of the two life stages and help to understand the haploid-diploid life strategy. Thus the results may be relevant also for conservation issues.
We investigated the patterns of macroalgal distribution in the Kattegat-Baltic region. Salinity played a significant role, but the influence of dispersal barriers was also significant. Furthermore, we found a strong numerical reduction of non-dominant species rather than dominant species. We also investigated patterns of macroalgal species diversity in Danish estuaries, species richness and abundance in communities in coastal waters, long-term-changes in a Danish estuary, and relationships between local abundance and range size of macroalgae in Scandinavia. The latter investigation shows that macroalgae obtain positive abundance-range size across large marine areas probably because of their continuity and restricted specializations of species composition among sites. The pattern of marine macroalgae is in contrast to the situation for terrestrial plants and animals, which do not exhibit significant abundance-range relationships in diverse and patchy terrestrial landscapes, but show positive relationships only within specific habitats.
Microsatellites are regions (loci) within an organism's genome that display a high degree of variability and therefore can be used to identify population substructure. In some cases, PCR primers developed to identify and quantify microsatellite loci in one species can be used in closely related species. In seaweeds, however, the degree of cross-reactivity is low and primers tend to be species-specific. Consequently, the primers we developed for use in the seaweed F. serratus can only be used for this species and in hybrids between F. serratus and another Fucus species.
Other researchers will benefit from our primers when they address questions of population substructure of F. serratus in other geographic areas. The collective studies on F. serratus can be instrumental in addressing various conservation issues, such as the development of Marine Protection Areas and European Heritage sites of high Marine Biodiversity.
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